1. Field of the Invention
The invention relates to a focal plane plate for a high-resolution camera with light-sensitive semiconductor sensors, and to a method for adjusting the housed light-sensitive semiconductor sensors on the focal plane plate.
2. Description of the Related Art
High-resolution cameras with light-sensitive semiconductor sensors are used, for example, for aerial photographs, where they replace conventional aircraft cameras with large-format films. The light-sensitive semiconductor sensors are designed as CCD components in this case. xe2x80x9cCMOSxe2x80x9d cameras have also recently become known, and have been developed as an alternative to CCD cameras, which have been known for a long time. These and similar sensors can generally be referred to as light-sensitive semiconductor sensors. The problems described below in connection with CCD components also apply analogously to the other light-sensitive semiconductor sensors.
In a high-resolution CCD camera, the CCD component designed as a linear array or matrix and is arranged to that end in the film plane, i.e., the so-called focal plane, as a result of which the intermediate step of film developing that is required in conventional film cameras is obviated. The entire image information is available immediately on-line and in real time digitally. However, replacing the film of an aerial-photograph camera by a focal plane equipped with CCD components entails a variety of difficulties.
The CCD components and the electronics near the sensors consume electrical energy, which is converted to heat as power loss. In addition, they have to be operated with a constant operating temperature under very different ambient temperatures. These problems are currently resolved by constructing a special focal plane baseplate which is composed of a material which is compatible with respect to expansion with regard to the CCD chips made of silicon, and is coupled to a heat sink in order to keep the temperature of the focal plane constant. Such focal plane hybrids are equipped with chips that have already been separated and subjected to preliminary testing. As the number of pixels in the CCD linear arrays increases, the chips become very expensive to fabricate and are difficult to handle on account of their mechanical and electrostatic sensitivity. The few manufacturers globally which are able to produce CCD linear arrays with 12,000 or more pixels trade only in housed CCD linear arrays. Workers developing focal planes with high-resolution CCD linear arrays therefore have to work with housed linear arrays.
Conventional housed CCD components are produced carefully in mechanical terms; nevertheless, the tolerances between housing geometry and chip position are so large that when they are mounted on a planar surface, the image-recording pixels no longer form a planar surface. Rather, the deviations in the image plane are so large that sharp imaging of all the pixels in a linear array, as well as of corresponding pixels in different linear arrays, is no longer possible. In this case, the tolerances of the housings are of the order of magnitude of +/xe2x88x92250 xcexcm. On account of the optical system, however, only deviations of approximately 10 xcexcm are permissible in order still to ensure sharp imaging of all the pixels.
The present invention is based on the technical problem of providing a focal plane plate for a high-resolution camera with housed light-sensitive semiconductor sensors, and a method for adjusting the housed light-sensitive semiconductor sensors on the focal plane plate so that all the pixels of the light-sensitive semiconductor sensors have virtually the same imaging sharpness.
According to an embodiment of the invention, the focal plane plate is designed with adjustment elements at the arrangement locations of the housings of the light-sensitive semiconductor sensors. These adjustment elements can then be processed in a complementary fashion in accordance with the positional deviations of the pixels with regard to the undersides of the housings. The result is that the top side of the housings and thus the sensor pixels lie virtually in one plane E.
Instead of a continuous adjustment element, it is also possible to use a plurality of individual adjustment elements. In order to carry out the adjustment, the housed light-sensitive semiconductor sensors are measured, preferably contactlessly, to determine the position of the surface of the light-sensitive semiconductor sensors with respect to the underside of the housings. The surface of the adjustment elements is subsequently treated by means of material-removing method steps in a complementary fashion with respect to the housing forms such that the pixels of the light-sensitive semiconductor sensors lie approximately in one plane in the assembled state. The housed light-sensitive semiconductor sensors are in this case measured for example by means of a microscope on whose support an end gauge is arranged in a defined manner. The housed light-sensitive semiconductor sensor is then arranged on the end gauge and its surface is measured in terms of height.
In a preferred embodiment, the adjustment elements are designed as parallelepipedal islands or inserts. The parallelepipedal islands may either be formed integrally from the focal plane plate or be arranged as separate elements on the focal plane plate, whereas the inserts are arranged mechanically in cutouts in the focal plane plate. The inserts are preferably attached in a mechanically releasable manner in the cutouts, so that they can be exchanged as required.
In a further embodiment, the housings and the complementarily adapted adjustment elements are permanently connected to one another. On the one hand, this provides a fixed assignment which cannot be lost even in the event of exchange and, on the other hand, this enables good thermal contact between the adjustment elements and the housings, given suitable connecting means. In principle, therefore, the housing and the insert may also be designed in an integral fashion. In this case, the adjustment is effected by means of additional adjustment webs in the cutout in the focal plane plate.
In another embodiment, the focal plane plate is designed with holes which are part of a cooling device. Various implementations are possible for this purpose. On the one hand, the holes may be designed to be continuous, so that, by way of example, a coolant can be pumped through the focal plane plate. A meandering passage through the focal plane plate is also possible but is somewhat more difficult to realize in terms of production engineering. If heat pipes are used for heat dissipation purposes, then the holes need not be continuous but rather reach only as far as the light-sensitive semiconductor sensors. The holes are preferably passed into the adjustment elements, with the result that the heat is dissipated directly at the heat source. In the case where the adjustment elements are designed as inserts the holes in the focal plane plate are made such that they extend into the cutout. The inserts are then likewise designed with a hole. These holes, which are coordinated with one another, then form a continuous duct in which a respective heat pipe can then be arranged.
In yet another embodiment, the focal plane and/or the adjustment elements and/or the housings of the light-sensitive semiconductor sensors are composed of materials which are compatible with respect to expansion, thermal stress that might otherwise adversely affect the adjustment thereby being prevented.
In still a further embodiment, the adjustment elements are composed of a material having a greater thermal conductivity than that of the focal plane plate. This is advantageous whenever the light-sensitive semiconductor sensors are to be kept at an operating temperature which is lower than the ambient temperature. As a result of this, less parasitic heat is coupled from the focal plane plate into the adjustment elements.
This is not necessary in the case of embodiments in which the light-sensitive semiconductor sensors operate at ambient temperature, with the result that the focal plane plate and the adjustment elements and the housings are then preferably composed of the same material. Aluminum nitride ceramics have proved to be a particularly good material.
In a further preferred embodiment, the focal plane plate is plated through in the region of the contact pins. This enables the electronics which are near the sensors to be arranged on the underside of the focal plane plate. As a result of this, on the one hand, an extremely compact unit is produced and, on the other hand, the additional electronics, which also produce a heat loss, are sufficiently decoupled thermally from the light-sensitive semiconductor sensors.
In order to obtain contact pins of sufficient length, the contact pins arranged on the housing are artificially lengthened which enables conductor tracks to be applied to the side areas of the inserts. Additional separate contact pins can then be attached to the conductor tracks in an electrically conductive manner. In this case, the conductor tracks are preferably printed on silver-palladium pastes which have proven to be worthwhile, particularly in the case of aluminum nitride ceramics. In addition, a temperature sensor may be arranged on the adjustment elements which can be used, in particular, for regulating a cooling device. However, the temperature is always a parameter of interest and is therefore desirable to detect
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.